Field of the Invention
This invention relates to hydrocarbon refining. More particularly, it concerns a process for catalytically sweetening hydrocarbons.
Description of the Prior Art
Many refinery hydrocarbon streams including feedstocks, fractions and products contain minor amounts of mercaptans (thiols) and hydrogen sulfide (H.sub.2 S). These sulfur-containing materials impart objectionable odors and corrosiveness to the hydrocarbons. Hydrocarbons containing these materials are referred to as "sour" hydrocarbons and are commonly treated to remove the mercaptans or to convert them to nonodiferous, noncorrosive disulfides, thereby forming a "sweet" hydrocarbon.
The conversion of mercaptans to disulfides has conventionally employed molecular oxygen as a reactant with a sweetening catalyst usually containing copper. The overall chemical reaction involved in the conversion of mercaptans to disulfides is: EQU 2RSH+1/2O.sub.2 .fwdarw.RSSR+H.sub.2 O
wherein R is a hydrocarbon radical, typically an alkyl.
Two representative patents concerning this process of the art or the catalysts employed in it are U.S. Pat. Nos. 3,809,643 issued May 7, 1974 and its continuation 3,907,666, issued Sept. 23, 1975.
Australian Pat. No. 159430 (Published 24 April 1952) discloses that free oxygen, together with a supported copper salt, can sweeten a hydrocarbon. U.S. Pat. No. 3,454,488 discloses a catalyst for use in a free oxygen-based process as does U.S. patent application Ser. No. 301,532 filed on Sept. 14, 1981. That application is commonly assigned herewith.
These prior processes require elevated pressures to get adequate oxygen into the feedstocks. This calls for compressors and pressure-capable equipment which can be expensive and complicate the refining process. Moreover, the art notes that the amount of O.sub.2 added as molecular oxygen must be controlled if undesired oxidation of the feedstock itself and gum formation are to be avoided.